1. Field of the Invention
This invention relates generally to a packet-switched satellite communication system and, more particularly, to a hiearchical downlink scheduler for a spot-beam processing satellite.
2. Discussion of the Related Art
A packet-switched network differs from a circuit-switched network in that the latter requires a physical circuit between communicating users. Thus, the circuit is committed, even if no information is being transmitted, until communcation ends between the users. Generally, the packet-switched concept avoids this inefficient use of a communication link resource by breaking communication into data packets (i.e., data cells) with address information, and then transmitting all of the data packets, regardless of source or destination, over the critical circuit. Routing is performed on the data packets as information passes between users.
Asynchronous transfer mode (ATM) is one of a class of packet-switching technologies that routes data packet traffic via an address contained within the packet. ATM is a fast packet or cell relay concept that uses a short (e.g., 53 byte) fixed-length cell to transmit information across networks. ATM is defined in the overall broadband ISDN standard by ANSI and ITU-T standards committees. While ATM is being deployed for terrestrial network systems, it is still an evolving technology within satellite communication systems.
In the context of satellite communication systems, an ATM-based satellite link has a limited number of circuits (e.g., uplinks and downlinks), and yet still handles large volumes of data packet traffic. An efficient and fair technique of passing the packets from the router (or cell switch) to the downlink is required in a satellite link. In this case, xe2x80x9cefficientxe2x80x9d refers to minimizing the downlink bandwidth that is unused among the various users and service classes, whereas xe2x80x9cfairxe2x80x9d refers to an approximate equal allocation of bandwidth to equal paying users. A scheduler for passing cells from the cell switch to the downlink modulator is the critical point for increasing the efficiency of the satellite link. There are several unique characteristics of a satellite system, such as hopping beams and different coding rates, which make the scheduler different from existing terrestial networks.
Therefore, it is desirable to provide an innovative hierarchical scheme for scheduling data cell throughput from the cell switch to the downlink modulator in a satellite system. A downlink scheduler implementing such a scheme will thus provide more efficient and fair scheduling of downlink resources, while maintaining certain Quality of Service guarantees. In addition, the scheduler enables real-time purchasing and selling of wholesale bandwidth based on the availability of resources and the demand of various customers.
In accordance with the present invention, a downlink scheduler is provided for scheduling the downlink transmission of data cells in a spot beam processing satellite. The downlink scheduler includes a beam selector for selecting one of the spot beams associated with the satellite, a plurality of wholesale selectors for selecting one of a plurality of wholesalers, such that each of the wholesale selectors is associated with one of the spot beams, and a plurality of retail selectors for selecting one of a plurality of retail connections, such that each of the retail selectors is associated with one of the wholesalers. The downlink scheduler then passes at least one data cell from a selected retail connection to a downlink modulator, thereby scheduling the downlink transmission of data cells in the satellite.